1. Field of the Invention
The invention relates to an optical waveguide having a region to which interacting means, such as a dopant or electrode, are applied for controlling an optical property of the a waveguide.
2. Background of the Related Art
It is known to apply dopant to a portion of the waveguide, for instance to form a p-n or p-i-n diode across the waveguide for injecting charge carriers into the waveguide and thus altering the effective refractive index of the waveguide. By this means a phase modulator can be provided such as the phase modulator disclosed in WO95/08787. However, in designing such a device, a compromise has to be made between the desire to maximise the overlap between the charge carriers injected into the waveguide and the optical mode therein while minimising the attenuation caused by overlap between the optical mode and the doped regions.
It is also known to apply a metal layer to a waveguide, e.g. to provide an electrical contact, or a heating element thereon. Again, there is a desire to position this as close as possible to the optical mode to maximise the effect of the electrical contact and/or heating but, on the other hand, the metal layer needs to be spaced from the optical mode so as to minimise absorption of one or both of its constituent TM or TE modes by tha metal layer.
There thus remains a need to be able to apply interacting means, such as dopant or an ohmic contact, to a waveguide without the interacting means itself causing substantial perturbation, such as attenuation or polarization, of an optical wave carried by the waveguide.